INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2019

The reconciliation between federal income taxes at the statutory U.S. federal income tax rate and the Company’s income tax expense for the year is as follows:



(in thousands)	December 31, 2019			December 31, 2018
Tax benefit at statutory rate	$	(23,591	)	$	(20,608	)
Other	(294		)	128
Stock based compensation	2,674			2,213
Issuance costs on warrants, private placement option, and preferred stock	4,657			—
Deferred tax valuation allowances	19,542			21,606
Research and development credit	(2,988		)	(3,339		)
Income tax expense	$	—		$	—

Significant components of deferred taxes

Significant components of the Company’s deferred taxes as of December 31, 2019 and 2018 are as follows:



(in thousands)	December 31, 2019			December 31, 2018
Deferred tax assets (liabilities):
Federal net operating loss carryforward	$	81,960		$	63,624
Stock compensation	3,270			4,533
Intangible assets	8,077			8,392
Research and development credit	16,601			13,612
Operating lease right-of-use assets	(1,229		)	—
Lease liabilities	1,538			—
Other	2,336			2,858
Total deferred tax assets, net of deferred tax liabilities	112,553			93,019
Valuation allowance	(112,553		)	(93,019		)
Net deferred tax assets	$	—		$	—

Summary of Net Operating Loss Carryforwards

Net operating loss carryforwards and research tax credits as of December 31, 2019 and 2018 are as follows:



(in thousands)	December 31, 2019		December 31, 2018
U.S. federal income tax net operating loss carryforwards	$	390,286	$	302,971
U.K. net operating loss carryforwards	$	—	$	2,424
U.S. federal research tax credits	$	11,348	$	8,939
Texas research tax credits	$	5,252	$	4,673